NoPasaran

Hi, everyone

I have 325x25 rear tyres (20") on a car that sits 1 inch lower than stock (H&R springs).
I have noticed that the inner part of rear tyres wears much quicker than outer part. Obviously I have negative camber on the rear axle.

Question is - do I need negative camber on rear axle?
Turbo is DD, and I do no track driving.

Thanks for suggestions!

Macster

The car needs negative camber on the rear tires. This negative camber does not account for the inner edge wear.

Rear toe is incorrect.

Next time you get new rear tires on the car have the car aligned. For now select stock settings if the springs do not interfere with the tech obtaining these.

When you take the car in have the gas tank full, all dead (junk) weight out of the car, and any spare tire/tool kit properly secured.

Be sure you get a *before* and *after* printout of the alignment settings.

NoPasaran

Thanks, Macster!

The tyres have 15000km on them.

So, you say I have too much toe out then? What degree of rear toe should I have - zero is probably the best?

And how come negative camber does not affect tyre wear? I thought, since the inner edge is, so to speak, more pressed to the ground by negative camber it would wear quicker.

I was planning to go and have an alignment now, with the current unevenly worn tyres. Would that be wise and if not - why?

P.S. I did not know Porsche 997 Turbo has a spare tyre. I can't even imagine where the tool kit is stowed, there is no space in that car but the front and back seats.

Macster

The alignment results will almost certainly be subpar with worn tires. A good tire alignment specialist should point this out.

When I took my 996 Turbo in to correct a bit of what proved to be front wheel toe out because the tires were worn the Porsche tech warned me the alignment results might *not* be up to the usual high standard. I acknowledged this and yet had him go ahead. The toe was causing tire howl that had me at one point convinced a wheel bearing was going, gone bad.

Your best bet is to replace the rear tires and if the fronts are worn evenly and have good tread left have the car properly aligned. If the front tires are worn then replace them too.

My info is the gas tank should be full, no junk in the car, and spare tire if any and the toolkit should be present and correctly secured.

Some places like to use ballast to mimic the driver's weight and some places don't bother. I've had the 996 Turbo aligned both ways and I can't tell the difference.

Oh, 15000km and worn out or nearly so is about right if the alignment it out. I went through a rear set of tires in under 9K miles with what proved to be a terrible alignment. The car felt ok though but oh the tire life was short!

By way of comparison the rear set of tires I had replaced last July had 23K miles on them even wear and 3mm of tread left. Had to replace them due to a puncture in the right rear tire.

For the correct amount of toe the alignment rack computer will know. The wheel alignment is displayed graphically and the Porsche tech adjusts until all the numbers are green.

Get a before and after printout.

Wheel alignment is funny. The settings are set with the car stationary and yet the alignment only matters when the car is moving.

So what looks "wrong" or what looks like it would cause excessive wear or other behavior does not.

Thus going down the road the wheels/tires assume a position that delivers good handling, good road feel, and good tire life and with even wear across the tread face.

If you get behind a Porsche you'll see the rear tires are quite flat on the ground. The negative camber appears to turn into nearly no camber. Sure you'll see pics of cars on the track under hard cornering with the outside tire flat or nearly so while the inside tire is showing big camber. A heavy foot and lack of LSD can have that inside rear tire spinning and inside tire wear occurs.

Same with toe. Toe in on the rack goes away when the car is going down the road. Suspension bushing firmness, tire size, and other factors all play a role so the tires/wheels assume an ideal or as nearly ideal position as they can.

NoPasaran

Thank you, Macster.

I go to Sportec. They did the tuning on my car and they have a new alignment rig installed last year, and they probably did the original alignment on the car years ago, when the 20" wheels were installed.